Besnoitiosis in Donkeys (AAEP 2011)

Besnoitiosis has recently been diagnosed in donkeys from several states on tissue and blood samples sent to Cornell University.

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Cases of a rare parasitic disease surfaced in U.S. donkeys in 2011, prompting a group of Cornell University researchers and colleagues to examine the condition—called besnoitiosis— more closely. One veterinarian described the disease, which is characterized by the development of cystic lesions both externally and in the throat and eyes, and weighed in on its detection and treatment at the 2011 American Association of Equine Practitioners convention.

"Besnoitiosis has recently been diagnosed in donkeys from several states on tissue and blood samples sent to Cornell University," explained Sally Ness, DVM, an internal medicine resident at the College of Veterinary Medicine’s Equine and Farm Animal Hospital. During her presentation at the convention, held Nov. 18-22 in San Antonio, Texas, Ness said the disease might be far more common in donkey populations than previously thought.

Besnoitiosis is caused by a protozoan parasite that is known to affect multiple host species worldwide. Cases are found primarily in Africa and Asia; however, recent outbreaks in European cattle populations suggest the disease could be spreading globally. Besnoitiosis in donkeys and horses is caused by Besnoitiabennetti, a coccidial parasite (a single-celled obligate intracellular parasite) that infects the animal, growing within tiny cysts in the skin, organs, and even the eyes of affected animals. So far, the only known cases of besnoitiosis in North America are in donkeys.

Ness and her team have examined donkey herds in the Northeastern and Northwestern United States with the goal of learning more about the clinical features of besnoitiosis and the best ways to diagnosis it. Currently, the mode of transmission is unknown, and there are no known effective treatments.

She relayed that her research confirmed besnoitiosis in "several donkeys," all of which had numerous lesions both externally (primarily on the face, nostrils, and ears)and in the nasopharynx. Histopathology on skin biopsies is the current gold standard diagnostic technique, however this method requires the examiner to correctly identify the often subtle lesions prior to testing.

To evaluate some new less invasive and potentially more reliable methods for diagnosing besnoitiosis, Ness and her colleagues performed IFAT (indirect fluorescent antibody testing) and immunoblot for serum antibodies to B. bennetti on all of these donkeys, using histopathology to confirm disease. One of the goals of their study is to validate a simple and noninvasive test that would be available to both owners and veterinarians.

Additionally, they tested ponazuril as a treatment for two of the affected donkeys for 37 days. The donkeys did not show any response to treatment, suggesting the drug "does not appear to be an effective treatment, at least at the dose and duration of treatment that we used," she explained.

"Infected individuals had significantly higher antibody titers to B. bennetti than did noninfected individuals, and we may soon be able to offer a serologic test for besnoitiosis in donkeys,” she concluded. “Such a test would be of great value to owners, as this appears to be emerging as a significant disease of donkeys in this country."

About the Author

Erica Larson, news editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in eventing with her OTTB, Dorado.

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